In 1970, the share of U.S. income that went to the middle class was 62 percent, while wealthier Americans received just 29 percent. But by 2010, the middle class garnered 45 percent of the nation's income, tying a low first reached in 2006, compared to 46 percent for upper-income Americans.

The new study reviewed 2010 data from the Census Bureau and Federal Reserve, defining "middle class" as the tier of adults whose household income falls between two-thirds and double the national median income, or $39,418 to $118,255 in 2010 for a family of three. By this definition, "middle class" makes up about 51 percent of U.S. adults, down from 61 percent in 1971.

Middle class shrunk by ~15% while their share of income shrunk by more than 25%. Seems likely that the 10% drop in "middle class" mostly ended up falling through the bottom of the range than floating out the top. That would mean the top tier got 50% more wealthy on overage. It's a bit tough to analyze this snapshot of data though since the middle class range isn't anchored and why I have to assume where the 10% that are no longer in the middle class went.

A few other statistics you might find interesting:

Since 2000, the median income for America's middle class has fallen from $72,956 to $69,487.

The Pew study is just the latest indicator of a long-term trend of widening U.S. income inequality. The Census Bureau reported last year that income fell for the wealthiest — down 1.2 percent to $180,810 for the top 5 percent of households. But the bottom fifth of households — those making $20,000 or less — saw incomes decline 4 percent.

Declining wealth: Median net worth for the middle class fell 28 percent over the last decade, from $129,000 in 2001 to $93,000, wiping out two decades of gains. Among upper-income families, net worth edged higher from $569,000 to $574,000. Lower-income families saw net worth fall 45 percent to $10,000.